Engines, including diesel engines, gasoline engines, natural gas engines, and other engines known in the art, may exhaust a complex mixture of air pollutants. The air pollutants may be composed of both gaseous and solid material, such as, for example, nitrous oxides (NOx).
Due to increased environmental concerns, exhaust emission standards have become more stringent. The amount of particulate matter and gaseous pollutants emitted from an engine may be regulated depending on the type, size, and/or class of engine. In order to meet these emissions standards, engine manufacturers have pursued improvements in several different engine technologies, such as fuel injection, engine management, and air induction, to name a few. In addition, engine manufacturers have developed devices for treatment of engine exhaust after it leaves the engine.
Engine manufacturers have employed exhaust sensors, such as oxygen sensors and NOx sensors, which may detect levels of exhaust constituents on which engine control may be based. For example, systems have been developed that include an oxygen sensor, which may measure the amount of oxygen in the exhaust. The level of oxygen in the exhaust may be indicative of whether the air-fuel ratio (AFR) is within desired specifications. Engine control parameters, such as those affecting AFR, may be varied based on oxygen levels measured by an oxygen sensor.
Other systems may employ a NOx sensor for measuring the level of NOx in the exhaust. Systems have been developed that control engine parameters based on measurements taken by a NOx sensor. For example, one such system is disclosed by U.S. Pat. No. 6,370,473 issued to Yasui et al. on Apr. 9, 2002 (“the '473 patent”). The '473 patent discloses a system, wherein a NOx sensor is utilized to measure the amount of NOx in the exhaust. The '473 patent further discloses that an air-fuel ratio (AFR) of the combustion mixture may be controlled by controlling fuel supply based on the measurements taken by the NOx sensor.
While the system of the '473 patent may include a NOx sensor and may be configured to control one or more engine parameters based on measurements taken by the NOx sensor, NOx levels may be dependent on a number of different operating parameters. Except for air-fuel ratio, the system of the '473 patent does not control any of these different operating parameters based on the NOx measurement. In situations where an undesireable NOx level is due to an operating parameter other than air-fuel ratio, the system of the '473 patent may not be capable of rectifying the undesireable NOx level. For example, the '473 patent does not measure charge density, which may have a significant effect on NOx levels. Accordingly, if an undesirable NOx level is due to variations in charge density, the system of the '473 patent would not be able to detect the source of the problem, and therefore would not be able to correct it.
The present disclosure is directed to solving one or more of the problems described above.